1. Field of the Invention
The present invention relates to an image reading apparatus for reading an image of a document sheet and an image recording apparatus for recording an image on a recording sheet.
2. Related Background Art
A printer having a recording head such as an ink jet head or a thermal head mounted on a carriage and recording an image on a record sheet by the recording head by moving the carriage has been used as an output device of a personal computer and a word processor.
In such a printer, it has been proposed to mount an image reading unit having a photo-electric conversion function in place of the recording head on the carriage to read an image of a document sheet for use as a scanner for inputting a read image data to the personal computer or the word processor.
In order for such a printer to fully function as the scanner, it is required to not only read the image of the document sheet as a black and white bi-level image but also read it as a multi-level image having black and white as well as half-tone densities as the processing function of the personal computer is enhanced.
However, in the reading of the multi-level image, the image processing of several times as much data amount as that required for the reading of the bi-level image is needed, and in order to allow both the bi-level image reading and the multi-level image reading, the system should be configured to meet the multi-level image reading operation which requires a large amount of data. This leads to the increase of a memory capacity and the increase of a processing time. When the system configured to fit the multi-level image reading operation is frequently used in the bi-level image reading, the construction for the multi-level image reading is wasted, which is not suitable.